In vehicle exhaust systems, it is desirable to provide a pipe joint with high pull-apart strength and with a good fluid seal between the pipes. It is becoming increasingly important to achieve greater reliability and uniformity in providing exhaust pipe joints with a good fluid seal.
In the Cassel U.S. Pat. No. 4,629,226, granted Dec. 16, 1986, a pipe lap joint is disclosed which provides a collapsible sealing zone in the outer pipe. This is achieved by providing a pair of intersecting end-to-end slots in the outer pipe which provide relief for circumferential contraction of the sealing zone within the overlap region of the pipe ends. A band clamp is disposed around the outside pipe and covers the inboard slot. When the band clamp is tightened around the outside pipe the sealing zone of the outer pipe is collapsed into close fitting engagement with the inner pipe. The intersecting outboard and inboard slots are circumferentially offset with the adjacent sidewalls in substantial alignment with each other and with the inner end wall of the outboard slot in substantial alignment with the outer end wall of the inboard slot. With this alignment and with the sidewalls and end walls of the slots being rectilinear, an inner corner of the outboard slot makes a point-to-point intersection with an outer corner of the inboard slot. With this structure, only a very small amount of collapse of the outer pipe is necessary to cause a sealing engagement between the inner end wall of the outboard slot and the outer end wall of the inboard slot.
The Cassel et al. U.S. Pat. No. 5,588,680, granted Dec. 31, 1996, discloses a pipe lap joint for vehicle exhaust systems in which a pair of non-intersecting end-to-end slots are provided to afford relief for circumferential contraction of the sealing zone within the overlap region of the pipe ends. With this construction, precise location of the adjacent corners of the slots is required and the sidewalls and end walls, which form the corners, are rectilinear. In this pipe joint, a fluid seal is obtained upon tightening of the band clamp on the outer pipe even though there is no substantial contraction of the sealing zone by collapse of the slots because a frangible bridging segment of the pipe wall extends between adjacent corners of the slots. Thus, the slots are isolated from each other when the frangible bridging element is either only slightly deformed or when it is completely fractured by collapse of the overlap region of the outer pipe.
U.S. Pat. No. 6,089,624 issued to Cassel et al. on Jul. 18, 2000 discloses a pipe lap joint in which an outer telescoping pipe end has a collapsible slot that includes a serpentine slot defined by a pair of inwardly protruding teeth. The telescoping end is overlapped onto a second, diametrically-smaller pipe end and a band clamp is placed about the telescoping end such that it overlaps at least a portion of the collapsible slot. The band clamp is then tightened which draws the protruding teeth together, thereby closing the slot. The disclosure of U.S. Pat. No. 6,089,624 is hereby incorporated by reference.
For pipes having reasonably good dimensional tolerances, a collapsible slot having a specific width can be designed in accordance with the diameters of the two pipe ends so that, during tightening of the band clamp, the slot collapses partially or completely but only enough to deform it slightly, if at all. However, the inventors have found that, where there is a greater degree of variability between pipe end diameters from one set of pipes to the next, the amount of circumferential closure of certain slots can be more limited than is desired due to the engagement of some slot features such as teeth with the opposite wall of the slot, and this can lead to situations in which the outer, telescoping pipe end does not sufficiently clamp down on and seal against the inner pipe end.
Thus, it is a general object of this invention is to provide a pipe lap joint with an improved sealing zone, particularly one that is well suited to accommodate variations in pipe end diameters.